In a society in which energy consumption is directly related to economic and material well-being, it is becoming increasingly evident that the cost of energy, both in environmental and fiscal terms, is a foremost limiting economic factor. For example, as petroleum based energy sources dwindle and become more expensive, increasing consideration is given to the use of coal and nuclear fission generated power. The damage that might be done to the ecosphere in exploiting these latter energy sources, as well as the cost in developing these sources, may well prove to be an insurmountable burden.
One energy source which has been known for years but which has been relatively undeveloped is geothermal power. It has been calculated that the latent heat within the earth itself is sufficient to meet all of the energy needs of all of civilization for centuries to come. However, the methods developed for retrieving geothermal energy are relatively unsophisticated and relatively unsuccessful. The following patents exemplify the state of the art in recovering geothermal energy:
3,857,244 3,911,683 PA1 3,903,700 3,957,108 PA1 3,908,381
The oldest and most obvious method of recovering geothermal energy is to inject water into heat-bearing rock strata and to recover the steam generated in this process. It has been found, however, that recovering steam from rock strata is not an easy task. Furthermore, the steam often carries corrosive elements such as sulphates, mineral contamination, and the like, which must be removed from the steam before it can be used in a working apparatus. Furthermore, the water injecting pipes and the steam recovery manifolds are subject to corrosion and have a very short operational life.
Another method of recovering geothermal heat is to place a passive heat conducting pipe into a geothermal well. The upper end of the pipe extends into a heat recovery system such as the water boiler, thereby overcoming the corrosion and contamination problems of water injection systems. The major drawback of such a passive heat transfer system is that the heat transfer capacity is very limited; also, it is difficult to arrange such a passive heat transfer system to respond immediately to increased energy demands, due to the thermal inertia of the heat transfer pipe.
Another geothermal energy recovery technique involves the use of a working fluid in a closed cycle. In such systems, the working fluid is pumped to the well bottom where it absorbs latent geothermal heat. The pumping action then drives the working fluid to the earth's surface, where it is pumped through a heat exchanger such as a water boiler or the like, thence through a condenser and then back into the well. In such prior art systems, the working fluid may be water, or carbon dioxide. In either case, the use of pumps to move the working fluid, together with the use of vapor condensers, preheating heat pumps, and the like, requires a very extensive and expensive apparatus. Thus, the potentially free energy provided by geothermal heat is made quite costly.